Insulator



Patented Oct. 1, .1929

UNITED STATES PATENT OFFICE HAROLD B. SMITH, OF WORCESTER,MASSACHUSETTS, ASSIGNOR TO WESTINGHCUSE ELECTRIC & MANUFACTURINGCOMPANY, A CORPORATION OF PENNSYLVANIA msuna'ron Application filed May10, 1922. Serial No. 559,743.

My invention relates to insulators and particularly to insulators forsupporting high voltage conductors.

One object of my invention is to provide a high-voltage insulator thatshall have a relatively higher wet to dry arc-over voltage ratio thanheretofore attained and a wet areover voltage comparable with dryarc-over voltages heretofore customary.

Anotherobject of my invention is to so remove the drippings ofprecipitated moisture, such as rain or snow, from the arc-over zone inthe more intense dielectric field directly between the terminals of aninsulator as to largely eliminate the drippings as factors in thedetermination of the wet arc-over voltage value at which the insulatorwill break down and to thus increase wet arc-over voltages for givenspacing between terminals.

A further object of my invention is to provide a high-voltage insulatorthat shall be simple and durable in construction, economical tomanufacture and effective in its operation.

Whilemy invention is applicable to highvoltage insulators of variousforms, it is par ticularly adapted for employment with an insulator ofthe type set forth in my copending application,'Serial No. 548,818,filed April 1, 1922, and assigned to the Westinghouse Eleotrio andManufacturing Company, for a more thorough understanding of whichreference may be had.

Heretofore. to the best of my knowledge, all outdoor insulators andsimilar devices have been subjected to flashover at very greatly n.-duced voltage values under wet conditions as compared with dryconditions. This is true, even'whore the upper unit is snaped toconstitute a rain shed. l'iecause the drippings from rain or snow in afield of high potential gradieut cause localized concentration of thestresses in the dielectric field starting thewet and dry conditions andto increase the wet arc-over voltages as compared with those heretoforesecure In practicing my invention, I provide a weather protective memberthat is constructed of such material and shapeas to not unduly attractthe electrostatic lines of force from a given or controlled path orfield between the special metallic or other terminals of'an insulatorand that is also of such shape and relation to the insulator as toremove the drip pings a sufficientdistance from the positions ofhigh-potential gradient in the field as to avoid causing an excessivelylocalized concentration of the electrostatic stresses.

In the above mentioned manner, the arc over voltage values aremaintained more nearly equal under both wet and dry conditions.

Figure 1 of the accompanying drawing is a side View, partially inelevation and partially in section, of an insulator embed, my invention,and

Fig. 2 is a similar view of a modified form thereof.

Referring to Fig. 1, an insulator for which my invention is adapted maycomprise, in general, an elongated insulating member upper and lowerterminal members 2 and respectively, and upper and lower electr c staticflux distributing members 4 and 5, re spectively.

The insulating member 1, preferably of relatively small diameter, may bea rod or tube of wood, molded fibre or any other suit i able insulatingmaterial having ends of sub stantially frusto-conical shape, orotherwise suitably formed. for the reception of metal members 8 that maybe attached thereto, as by swaging. The members (3 may be provided withscrcw-threadml studs 7 for attachn'icnt lo the terminal members i and 3.

The upper electrostatic flux-distributingand-directing member-'4, shownin Fig. l of inverted howl-shape, may be provided with a portion 8 ofinverted cup-slums, having a central recess for positioning it over theup per stud 7. and be held in position between the member 0 and theterminal member 2. The

member 1 is provided with a rounded lower edge 9 of relatively greatradius.

The lower electrostatic stress-distributingand-directing member 5 isformed as an annulus having toroidal surfaces 10 of relatively greatradius and a central opening 11 of larger diameter than the insulatingmember 1. A bracket 12, having a collar 14 secured to the lower member 6and rounded arms extending between the collar l l and the member 5, isprovided to hold the latter in position.

A conductor 15, which the insulator is adapted to support, maybe coveredby a conducting sheath or jacket 16 of relatively great length anddiameter to avoid the concentration of electrostatic flux on theconductor adjacent to the insulator and be secured to the latter by aclamp 17 As set forth in the above-mentioned c0- pending application,the members 4 and 5 may be variously constructed so long as they areconducting on certain of the surfaces thereof in a manner to direct theelectrostatic flux field substantially as indicated by the dotted lines.The field is thus directed to be of shortest distance along a line 18and to be so gradually decreased toward the center of the insulator asto constitute a substantially hollow tubular field through which theinsulating member extends.

As pointed out in my co-pending application, the above-describedarrangement prevents the impingement of arcs against the insulatingmember 1 and so simultaneously definitely directs and widely distributesthe flux as to increase the arc-over voltage value of the insulator to apoint not hitherto attained in insulators of similar weight anddimensions.

It has been found that, under wet conditions, the accumulation of waterdrops on the upper unit of an insulator, such as on the edge 9, causeslocalized concentration of the electrostatic field, with the resultantflashover at values much below the dry arcing voltage value of theinsulator.

To correct the above fault, I propose the removal of the drippingportion or edge of an insulator from the arc-over zone in the fluxfield. This has been accomplished by providing a protective shed or hood19 over and aroundthe member 4. This has been attempted before butalways in such a manner as to permit the water to drip in or near thearcing path and in a field of high potential gradient. The provision ofmeans for placing the terminal under the protective hood avoids thiscondition.

In this instance, the hood 19 comprises an inverted bowl of a materialwhich may have higher resistance than the member a and is shaped andrelated to the flux field to have, over a ortion of its surface, allpoints substantial 1 coincident or nearly coincident,

with an equipotential surface. Being out of the main electrostatic fluxpath and having less attraction for the electrostatic lines, the

water drops, at the lower edge of the hood 19, are in a field of lowerpotential gradient and do not so greatly tend to locally concentrate thefield. Thus, when fiashover occurs, it will occur under desirableconditions between the members 4: and 5 irrespective of the weather.

As shown in Fig. 2, in which corresponding parts are designated bycorresponding reference characters, the upper electrostatic fluxdistributing and directing member 4a is similar to the lower member 5.

It will be understood that various modifications as to the size andshape of the members 4 and 5 as well as various combinations of themembers may be efl'ected within the spirit and scope of t e invention.

In accordance with my invention, a, sim is compact insulator of morenearly equal e ectiveness under wet and dry conditions is obtained, thatalso increases the wet flashover voltage values materially above wetflashover voltage values heretofore attained.

While I have shown and described particular forms of my invention,changes may be made therein without departing from the spirit and scopethereof, as set forth in the appended claims.

I claim as my invention:

1. An insulator comprising an elongated insulating member, an uppstrterminal mem her having a. conducting su antially toroidal surface ofrelatively great area surrounding the insulating member in widelyradiallyspaced relation thereto at a position downwardly removed fromthe upper end thereof, said surface mer ing at its inner portion into aconducting sur ace of inverted substantially bowl shape, said upperterminal member also having a water-dnp portion disposedlaterally-outwardly beyond said toroidal surface, and a lower terminalmember having a conducting substantially toroidal surface of relativelygreat area surrounding the insulating member in radially-spaced relationthereto, the space surrounding the insulating member between that memberand the lower toroidal a of the upper terminal member.-

2. A high-voltage insulator comprising an elongated insulating memberand upper and lower terminal members therefor having substantiallytoroidal conducting surfaces of relatively great area disposed about theinsulating member in laterally spaced relation thereto to widelydistribute the electrostatic flux over said surfaces and to prevent theconcentration of the electrostatic field at the ends of the insulatingmember and to direct the electrostatic field to conform to a uniformsubstantially cylindrical zone having a Weakened longitudinal centralportion through Which the insulatin member extends, said upper terminalmem er having a water-dri portion disposed laterally outwardly beyon itstoroidal surface, the spaces surrounding the insulating member betweenthe latter and each toroidal surface and for relatively great distanceslongitudinally beyond the toroidal surfaces away from each other beingopen to prevent interference with the electrostatic field as directed bysaid toroidal surfaces with respect to each other.

. In testimony whereof, I have hereunto subscribed my name this 18th dayof April 1922.

16 HAROLD B. SMITH.

